Hydraulic booster brake system



Filed Jan.' 8. 1951 2 SHEETSfSl-{EET 1 Nov. 18, 1952 WLSTELZER 2,618,123

I HYDRAULIQ BOOSTER BRAKE SYSTEM ggg JNVENTOR.

Nov. 18, `1952 w, STELZER 2,"6ml8,123

HYDRAULIQ BOOSTER BRAKE SYSTEM Filed Jan. 8, 1951 zsmms-l--slmz'r 2 Patented Nov. 18, 1952 UNITED STATES PATENT OFFICE HYDRAULIC BOQSTER BRAKE SYSTEM William Stelzer, Summit, N. J;

Application January 8, 1951, SerialNo. 204,946

(Cl. (S-54.5)

4 Claims. 1

The invention relates to, a hydraulic booster brake system, and more particularly to a booster system for hydraulic brakes of automatic vehicles, where the brakes are operated by manual power augmented by the force of a power operated booster controlled in a, manner which characterizes this invention.

It is customary in the art to call the manually operated hydraulic pressure producing element the. master cylinder'. andl the power operated mechanism assisting the manually operated element the booster. This terminology is maintained herein though the functions of these elements arer different from present systems. The usual practice is to produce a primary hydraulic pressure with the master cylinder and to transmit it to the booster which then transmits an increased pressure to the wheelv cylinders to rtpl-ily the brakes. The effort of the booster is in response to the primary pressure received from the master cylinder. According to the new invention the master cylinder transmits fluid directlyy to the wheel cylinders, and the booster acts indirectly on the master cylinder to ease the manual effort. The reaction for controlling the booster is between the hydraulic pressure produced by the booster and the wheel cylinder pressure, or the boosted pressure. It is thus entirely divorced from the manual effort. By maintaining a predetermined ratio between booster effort and boosted pressure, the latter is automatically in a fixed relation with the manual eiort.

The advantages gained with the new construction are a considerable simplification of the control mechanism and the opportunity to. placethe fluid vreservoir with the booster unit so that the size of the master cylinder may be greatly reduced and it may be mounted in any position.

One of the objects of the invention is to eliminate the usual hydraulic trip valve from the booster and to provide a trip valve in the master cylinder to allow return of lluid from the wheel cylinders to the booster when the master cylinder is in the released position.

Another object is to place a residual pressure valve in the master cylinder in an arrangement where the control mechanism of the booster is not subject to the residual pressure in the wheel cylinders.

A further object is to provide a control valve mechanism for the booster that is operated by the initial movement of the master cylinder; i. e., the initial movement of the master cylinder may be used solely to operate the valve without actuating the wheel cylinders before the booster is energized. l

Other advantages and objectsof this. inventio-n will be apparent from the following description considered in connection with the accompanying drawings submitted for the purpose of illustration and not to dene the scope of the invention, reference being had for that purpose to the subjoined claims. In the drawings, wherein similar reference characters refer to similar parts throughout the several views:

Fig. 1 is a longitudinal cross-sectional view of the booster and master cylinder, the connections and the other elements completing the entire system being shown diagrammatically;

Fig. 2, a diagrammatic sectional view of a modied master cylinder for the same system;

Fig. 3, a diagram showing a modified form of the invention, the master cylinder and valve mechanism being shown in section; and

Fig. 4, a section through the valve mechanism of Fig. 3 showing a different position assumed in operation. Y

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of elements illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practised or carried out in different ways. Als-o it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not limitation.`

Referring to Fig. l, master cylinder I0 is operated by manual power through foot pedal II to transmit fluid through line I2 to wheel cylinders I3 of which only one is shown, line I2" leading to the others. The master cylinder comprises a cylinder I4 in which slides a piston I5 provided with a seal I6 and secured to a piston rod I l passing through seal I8 and bearing I9 to be connected with pedal ll by means of a clevis 2B and linl; 2I. The end of cylinder I4 is closed by a cap 22 retaining a perforated metal cup 23 serving as a gasket for the cap and asa seat for the residual pressure valve 24 held in a closed posi-- tion by a Spring 25 to maintain a residua1 or higher pressure in wheel cylinders I3 and in chambers 26 and 21 of the master cylinder. Fluid is permitted to ilow from the booster unit 23 and line 29. through. a Check valve 3B, seated by a very light spring 3|, into chamber 2l. A `trip valve 32 is provided within piston I5 and urged .into a closed position by a light spring 33. A pin 34 fastened t0 @up 23 serves to open valve 32 in the released position as shown, s0 that valve ball 32 is lifted from its seat and iluid may pass between chambers 26 and 21 through passage 35. The master cylinder piston is shown in the released or starting position into which position it is urged by return spring 36.

The booster unit 23 comprises a cylinder body 40 in whose bore slides a piston 4| having a primary seal 42 and a secondary seal 43, the latter sealing the fluid from reservoir 44 communicating with the space between the two seals through hole 45. Piston 4| has a piston rod 46 to be operated by a, booster motor comprised of a casing 41 secured to cylinder body 40, a cover 48, a diaphragm 49 clamped between l41 and 43 by means of a clamp ring 50, and a diaphragm plate secured to piston rod 46. A return spring 52` urges the booster piston and the diaphragm piston of the motor into the released or starting position, as shown. Diaphragm 49 divides the space within casing 41 and cover 48 into chambers 53 and 54, the latter being permanently connected through line 55 to a source of low pressure or vacuum 56. Chamber 53 is connected through line 51 to chamber 58 of valve body 59 clamped to cylinder 40 with a ring or spacer 69 and double diaphragm 6| interposed. The central portion of the latter is mounted on a double or differential piston 62 whose extension at the left serves as a valve to close oi the central passage 63 of a rubber faced vacuum or low pressure valve 64 urged into a seated position by a spring 65 subordinate to a stronger spring 65 urging piston 62 to the left to keep vacuum valve 64 open as shown. The chamber in which spring 65 is housed is in communication with the source of vacuum by means of line 61. This chamber is sealed against the atmosphere or against the source of air pressure by a diaphragm 68 serving also to balance the valve to reduce the effort required to operate the valve when the motor mechanism is to be energized. rI'he outer portion of diaphragm 68 is secured to valve body 56 by means of cap 69 having a connection 10 leading to the atmosphere or to a source of air pressure 1|. Chamber 12 of the booster cylinder is connected to line 29 leading to the master cylinder and it is also in communication with reservoir 44 through port 13 when the latter is uncovered in the released or starting position, as shown. The space inside of seal 6| is connected through line 14 to wheel cylinder line |2 and to chamber 26 of the master cylinder where the final pressure is produced.

The modied master cylinder in Fig. 2 comprises a cylinder body 15 in which slides a piston 16 whose piston rod passes through the end wall at the left. A by-pass 11 serves to establish communication between chamber 18 and 19 when the master cylinder is in the released or starting position. Line 14 from the booster leads directly into chamber 19 so that the residual pressure maintained by residual valve 24 is not transmitted to seal 6| of the booster, thus permitting spring 66 to be weaker so that the booster may start to operate at a lower master cylinder pressure.

The modified construction illustrated in Fig. 3 uses a master cylinder 80 having a bore 8| in which slides a piston 82 engaged by a push rod 63 actuated by a foot pedal 84. Since the illustration is diagrammatic, the seals have been omitted. In another concentric bore 85 slides a helper piston 56 connected to piston 82 by a piston rod 81 passing through wall 88 separating the two bores and forming expansible chambers 89 and 90 connected to wheel cylinders I3 through line 9| and to a valve unit 92 through line 93, respectively. A fluid reservoir 94 is an integral part of the master cylinder, in communication with chamber 89 through port 95 when the master cylinder is in the released position, as shown.

The valve unit 92 comprises a body 96 having a central bore in which slides a valve plunger 91 with pistons 98 and 99 at the left end engaging a double diaphragm |00 whose outer fianges are secured by a recessed ring |6| bolted or otherwise fastened between valve body 96 and a cover |02, the latter having a central bore to slidingly receive piston 99 and to house are turn spring |63 urging the valve plunger into the released position as shown. The valve plunger has a peripheral groove in Comunication with line 93 through passage |64. Valve 96 is provided with internal grooves |05 and |06, the latter being connected through line |01 with an accumulator or other source of fluid pressure |08. Groove |95 is connected to low pressure line |09 leading to sump or reservoir ||6 to feed make-up pump connected to accumulator |08 through check valve ||2. These pressure producing elements are indicated diagrannnatically only since their construction is well known, this type of pressure system having been used extensively in aircraft. The stepped bore of the valve body in which piston 98 slides is also in communication with low pressure line |09 and .groove |05 to prevent any possible pressure build-up against diaphrgam |66. Chamber ||3 within the latter is open to the hydraulic pressure produced in chamber 9S of the master cylinder through lines 9| and H4. While in this embodiment the fluid medium from the pressure source is considered as a liquid, itr is apparent that the principle is not changed if a compressible fluid is used.

Considering now the operation of the embodiment shown in Fig. 1, and assumingthe system to be in the starting position as shown, depression of the foot pedal by the operator causes piston I5 of the master cylinder to be moved toward the left to displace fluid from chamber 26 to the chamber Within diaphragm 6|, acting on the two differential pistons in opposite directions. Since the force on the large area is greater, piston 62 is moved toward the right to compress spring 66 and to allow vacuum valve 64 to close. When this valve is closed, chamber 53 of the motor mechanism is shut 01T from the source of vacuum or low pressure. Further movement of piston 62 toward the right under increased pressure from chamber 26 unseats the atmosphere valve which is part of piston 62, and thus opens up a passage from source of pressure 1| into chamber 58 and through line 51 to chamber 53 of the motor mechanism so that the latter is energized to push piston 4| toward the left, displacing uid from chamber 12 into chamber 21 to assist in the application of the master cylinder. The increased pressure in chamber 12 acting on piston 62 opposes the action of the hydraulic uid within diaphragm 6| so that when the pressure in chamber 12 is increased to be in a pre-determined proportion to the final or wheel cylinder pressure the air valve is closed again to prevent any further energization of the motor mechanism. The proportion between the hydraulic pressure generated by the booster and the hydraulic pressure produced by the master cylinder is dependent on the proportion of differential piston 62. According to the example shown the valve would be balanced, i. e., in a lap position, if the hydraulic pressure in chamber 12 is approximately two thirds of the hydraulic pressure prodlled by the master cylinder. vThis aeie'gias" may be best illustrated with gures. Assuming the cross sectional area of 'the large piston of 62 to be 3A square inch, and that of the small piston.

1A; square inch, then the effective area exposed to the hydraulic pressure from line 14 is 1/2" square inch. If the pressure in line 14 is 1000 p. s. i., the force is 500 lbs., urging piston 62 towards the right. Opposing this force is a hydraulic pressure of 666 p. s. i. in chamber 12 acting on an area of 3A square inch, producing a force of 500 lbs. Neglecting the action of the valve springs, the valves would then be balanced so that the power of the motor would not .be further increased. Since the manual effort is equal tothe diierence between the nal or combined effort andthe booster effort, the manual effort or Work in `this case is one third of the nal effort represented by the hydraulic pressure in the wheel cylinders, so that the booster ratio is 3:1. It will also be remembered that this is the ratio of the-areas of differential piston 62, whereby the small area represents the manual effort on the brake pedal and the large area the effort exerted to actuate the wheel cylinders. In this consideration the effect of piston rod |1 of the master cylinder has been neglected. Due to the smaller Volume displaced from chamber 26 in relation to the volume received in chamber 21 the iinal pressure is somewhat higher. Assuming now that the operator releases the brake pedal, the hydraulic pressure in chamber 26 is reduced by one third so that the hydraulic pressure in chamber 12 is able to push piston 62 towards the left to close the air valve and open vacuum valve 64 so that chamber 53 is open to vacuum or low pressure again. The master cylinder as well as the booster therefore immediately start their retractile movement to return to the original or released position, where valve 32 is forced open and piston seal 42 of the booster passes port 13 so that communication is established between reservoir 44 and wheel cylinders I3, with residual valve 24 maintaining a slightly higher pressure in the wheel cylinders than exists in reservoir 44. If a brake application is made during power failure, then the boostermotor` remains in the released position while the brakes are applied purely by manual power. In this operation fluid is drawn into chamber 21 from reservoir 44 via port 13 and past cup 42 and piston 4|, the latter having the necessary clearance to allow this bypass, as is now the practice in present day master cylinders. piston I5 when the brake pedal is released again,

the fluid from chamber 21 has to be pushed back into reservoir 44 through port 13. It may be noted that piston I5 of the master cylinder will always be permitted to return to the released position, allowing fluid to pass from chamber 21 into chamber 25 either past valve 32 or past the outer lip of seal I6 whenever the hydraulic pressure in chamber 26 is lower. The operation of the master cylinder, shown in Fig. 2, is similar to that described in Fig. 1. Piston 16 is pushed toward the right when the brakes are to be applied. The difference is mainly that in this construction the residual pressure in wheel cylinders I3 and line I2 is not transmitted to the chamber within seal 6I. By-pass 11 in principle is the same as valve 32.

In the operation of the modified structure in Figs. 3 and 4, depression of the brake pedal causes piston 82 to move toward the left, closing port 95 and displacing hydraulic fluid from chamber 89 into chamber ||3 of the Valve unit to move During the retractile movement of valve plunger 91 toward the left so that the groove in the latter becomes disconnected from valve groove |05 and then comes into communication With groove |06 to allow fluid under pressure from source |08 through passage |04 into chamber 90, thus assisting in the application of the master cylinder and thereby increasing the hydraulic pressure in chamber 89. This position of the valve is illustrated in Fig. 4. Though the pressure in source |08 maybe very high, and more or less constant, the action of the valve unit is such as to produce a pressure in chamber 90 that is in a predetermined proportion with the hydraulic pressure transmitted to the wheel cylinders. As soon as pressure is transmitted from source |08 tochamber 90, the pressure reacts against piston 99 of the valve plunger in opposition to the pressure in chamber I I3 to return valve plunger 91 to a lap position as soon as the booster pressure in chamber 90 is suiciently high. Release of the brake pedal with a consequent reduction in hydraulic pressure in chambers 89 and |3 causes plunger 91 to be moved towards the right by virtue of the hydraulic pressure acting on piston 99 in the chamber which houses spring |03. Plunger 91 accordingly assumes the released position again where the source of pressure is disconnected and where chamber 90 is open to low pressure or sump |I0 through passage |04 and internal groove |05. Pistons 99 and 98 constitute differential pistons as described in Eig. 1, and the explanations in regard to booster ratio apply in principle also to this construction. A further way of changing the booster ratio is inthe size of piston 86. It is obvious that by increasing the diameter of piston 86 and bore the booster ratio is increase-d and the manual effort reduced.

I claim:

1. In mechanism of the class described, a liquid pressure system including a manually operated master cylinder connected to transmit hydraulic iluid to wheel cylinders to apply the brakes, a booster comprising a hydraulic pressure producing device arranged and connected to transmit hydraulic fluid to said master cylinder to assist the manual actuation of said master cylinder, a motor operatively connected with said pressure producing device, a source of power to energize said motor, valve means to transmit power from said source of power to said motor, pressure sensitive means responsive to the hydraulic pressure produced in said master cylinder through the combined manual and power effort to operate said valve means to increase the power of said motor, means responsive to the hydraulic pressure produced by said pressure producing device to urge said valve means to reduce the power of said motor mechanism, and means to maintain a residual pressure in said wheel cylinders.

2. The construction in claim 1, wherein said means to maintain a residual pressure in said wheel cylinders is arranged intermediate said wheel cylinders and said master cylinder so that the residual pressure is limited to the wheel cylinders and is not imposed on said pressure sensitive means.

3. In mechanism of the class described, a manually operable master cylinder adapted to transmit hydraulic fluid under pressure to Wheel cylinders to apply the brakes, a hydraulic booster adapted to produce a hydraulic pressure and to transmit it to said master cylinder to assist in the operation of the latter, a motor arranged to operate said booster, a source of fluid presling communication of fluid from said source to said motor, and a diierential diaphragm responsive to the hydraulic pressure transmitted to said Wheel cylinders and operatively connected to urge said valve to increase the power of said motor, said diierential diaphragm being acted upon in an opposing direction by the hydraulic pressure produced by said booster to urge said valve to reduce the power of said motor.

4. The construction as claimed in claim 3, a fluid reservoir connected with said booster, and a passage from said reservoir arranged to be uncovered in the released position to establish communication with the fluid transmitted from said booster to said master cylinder.

' WILLIAM STELZER.

REFERENCES CITED The following references are of record in the le of this patent:

Number Re. 22,349 1,903,973 1,921,590 1,997,062 2,057,707 2,136,318V 2,275,697 2,328,684 2,343,698 2,352,357 2,353,755 2,373,272 2,383,682 2,398,165l 2,407,097

UNITED STATES PATENTS Name Date Stelzer July 13, 1943 Stelzer July 13, 1943 Boughton Apr. 18, 1933 Staude Aug. 8, 1933 Huiman Apr. 9, 1935 Carroll Oct. 20, 1936 RossmannV Nov. 8, 1938 Stelzer Mar. 10, 1942 Schnell Sept. 7, 1943 Parnell Mar. 7, 1944 Almond 1-.- June 27, 1944 Price Jfuly 19, 1944 Stelzer Apr. 10, 1945 Price Aug. 28, 1945 Stelzer Apr. 9, 1946 Porter Sept. 3, 1946 Piganeau Mar. 7, 1.95.0 

